Capital and Accumulated Other Comprehensive Income (Loss) (Redeemable Preferred Units) (Details) - USD ($) $ / shares in Units, $ in Thousands									12 Months Ended
	Oct. 10, 2019	Mar. 13, 2019	Sep. 14, 2017	Sep. 07, 2017	Aug. 07, 2017	Aug. 24, 2015	Mar. 26, 2014	Apr. 09, 2013	Dec. 31, 2019	Dec. 31, 2018	Apr. 01, 2019
Preferred Units [Line Items]
Liquidation preference									$ 1,456,250
Units outstanding (in units)									58,250,000	50,650,000
Balance (in thousands, net of issuance costs) as of December 31,									$ 1,434,420	$ 1,249,560
Preferred stock, liquidation preference per share/unit (in dollars per unit)									$ 25.00	$ 25.00
Preferred Stock, Redemption Price Per Share									$ 25.00
Series C Preferred Units
Preferred Units [Line Items]
Liquidation preference									$ 201,250
Preferred stock dividend per share amount (in dollars per share)			$ 1.65625
Units outstanding (in units)									8,050,000	8,050,000
Balance (in thousands, net of issuance costs) as of December 31,									$ 219,250	$ 219,250
Dividend rate percentage			6.625%
Series G Preferred Units
Preferred Units [Line Items]
Liquidation preference									$ 250,000
Preferred stock dividend per share amount (in dollars per share)								$ 1.46875
Units outstanding (in units)									10,000,000	10,000,000
Balance (in thousands, net of issuance costs) as of December 31,									$ 241,468	$ 241,468
Dividend rate percentage								5.875%
Series H Preferred Units
Preferred Units [Line Items]
Preferred stock dividend per share amount (in dollars per share)							$ 1.84375
Units outstanding (in units)										14,600,000
Balance (in thousands, net of issuance costs) as of December 31,										$ 353,290
Preferred stock, liquidation preference per share/unit (in dollars per unit)											$ 25.00
Dividend rate percentage							7.375%
Preferred Stock, Redemption Price Per Share											$ 25.00
Series I Preferred Units
Preferred Units [Line Items]
Liquidation preference									$ 250,000
Preferred stock dividend per share amount (in dollars per share)						$ 1.58750
Units outstanding (in units)									10,000,000	10,000,000
Balance (in thousands, net of issuance costs) as of December 31,									$ 242,012	$ 242,012
Dividend rate percentage					6.35%
Potentially dilutive Series J Cumulative Redeemable Preferred Units
Preferred Units [Line Items]
Liquidation preference									$ 200,000
Preferred stock dividend per share amount (in dollars per share)					$ 1.31250
Units outstanding (in units)									8,000,000	8,000,000
Balance (in thousands, net of issuance costs) as of December 31,									$ 193,540	$ 193,540
Dividend rate percentage				5.25%
Potentially dilutive Series K Cumulative Redeemable Preferred Units
Preferred Units [Line Items]
Liquidation preference									$ 210,000
Preferred stock dividend per share amount (in dollars per share)		$ 1.46250
Units outstanding (in units)									8,400,000
Balance (in thousands, net of issuance costs) as of December 31,									$ 203,264
Dividend rate percentage		5.85%
Series L Preferred Units
Preferred Units [Line Items]
Liquidation preference									$ 345,000
Preferred stock dividend per share amount (in dollars per share)	$ 1.30000								$ 1.30000
Units outstanding (in units)									13,800,000
Balance (in thousands, net of issuance costs) as of December 31,									$ 334,886
Dividend rate percentage	5.20%